Protein phosphorylation is the major mechanism for regulation of protein function in eukaryotic cells. Over 100 protein kinases have been described, greater than 32 of which are now known to be encoded by oncogenes (1). Elevated src and neu protein-tyrosine kinase activity in human colon and breast carcinomas illustrates the need for diagnostic reagents capable of recognizing activated oncogene-encoded protein kinases (2,3). In breast cancer the degree of neu gene amplification correlates with prognosis, i.e., the greater the amplification the worse the prognosis for disease relapse and patient survival (3). Since numerous regulatory proteins require phosphorylation for activation and nearly all known protein kinases are subject to autophosphorylation, it is proposed in Phase I to synthesize phosphopeptides to be used to generate antibodies directed against the autophosphorylation sites of the abl and src protein-tyrosine kinases and the raf protein-serine/threonine kinase. Such antibodies may specifically recognize the activated forms of these proteins, and thus may allow the early detection of oncogene encoded kinases. In Phase II, the feasibility of using these antibodies as diagnostic reagents for screening human tumors would be evaluated and selected antibodies would be used for formatting screens with which to detect activated oncogene-encoded protein kinases in human tumors or patient sera.